That's very simple: the food you ate potentially caused it.

These are the foods I'd cut out (from personal experience on thus very subject): Cow's milk (known to cause cold and flu-like symptoms when I was immunocompromised), gluten (the wheat here in America has links to schizophrenia), soy (a good way to get an imbalance of hormones for a legume), refined sugars (they have the same effects as cocaine or heroin), and seed oils (the chemicals in seed oils have the same effect as fluoride in the water supply).

Dr. Berry would advocate for a straight carnivore diet, though I do a form of modified paleo, and it's been working for me. The foods above, from what I've experienced, would cause almost anybody issues with their body.